Typically, a subject is monitored to detect subject's wakefulness or drowsiness for taking an action when the subject is falling asleep. For example, the subject may be a vehicle driver, a person watching television and so on. In case of the vehicle driver, driver's drowsiness or wakefulness is detected and alerts may be sent to the driver to increase the attention while driving. An existing driver vigilance monitoring method is to monitor driver's facial expressions captured using an RGB camera and determine a drowsiness state of the driver based on movements of various muscles in the driver's face. The RGB camera requires illumination for capturing the driver's facial expressions. Therefore, a flash source may be used by the RGB camera for capturing the driver's facial expressions which can distract the driver during night time. Further, this method may recreate the face of the driver to localize the eyes for detecting driver's wakefulness or drowsiness. Another existing driver vigilance monitoring method is to monitor deviation from lane markings on the road and alert the driver when such deviations rise to dangerous levels. However, this method may provide false alerts to the driver when the vehicle deviation from the lane markings is caused due to distorted movement of vehicle wheels.